[Radiance-dev] SPEED or no SPEED

Georg Mischler schorsch at schorsch.com
Sat Sep 17 10:22:07 CEST 2005

Hi all,

the recent efforts to compile under mingw have directed my attention
to an issue in Radiance that has bothered me for quite a while.
The makeall script (and consequently my SCons configuration) defines
a value of SPEED for every known platform. This is used as follows:

In px/clrtab.c, the closest color routines are activated when SPEED > 8.
The lowest SPEED setting in makeall is 80, so this test has become
rather pointless.

In px/neuclrtab.c, DEFSMPFAC is defined as 240/SPEED+3.
With the current values of SPEED, this ends up somewhere between 1 and 3.
If DEFSMPFAC was already defined before (eg. through a -Dxxx directive),
then it gets *redefined* to 30. This difference of about an order of
magnitude makes me thing that this also isn't what was originally

In rt/rv3.c, WFLUSH is set depending on SPEED. This is the only case
where I can still agree with the original intention, even if the
method fails in similar ways as with the other cases.

By principle, there's no way to determine the performance of the
target system at compile time. And one of the worst ways to even
try is by looking at the OS of the compiling system. I'm not sure
if this ever was a good idea, but it certainly isn't on todays
hardware/operating systems.

For clrtab.c, the test can be removed without further thought.

For neuclrtab.c, I assume that the original intention was a tradeoff
between performance and memory use. Since both criteria are not
really critical anymore, I suggest we find a value of DEFSMPFAC
that is optimal for the algorithm in most situations and leave
it at that.

For rv3.c, we could also just set a reasonable fixed value (as the
Windows version does). If we really want to optimize to the actual
performance of the machine, then we'll have to test its speed
at run time. I'm not sure if that's really worth the effort, though.

The goal in any case is to eliminate the compile variable SPEED.
Any objections or other comments?


Georg Mischler  --  simulations developer  --  schorsch at schorsch com
+schorsch.com+  --  lighting design tools  --  http://www.schorsch.com/

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